It is known to use external bone fixators to reduce fractures in bones such as with fractures of the tibia. Advances in fixators have been made in terms of avoiding the infections that can be caused by use of bone pins that penetrate beyond the bone cortex such as into the tibial canal, or completely through the bone. In these devices, the bone pins typically have a distal bone engaging end having a split prong configuration for tight gripping of the bone surface. Herein, the term non-invasive pins means that the pins do not penetrate the bone canal or the cancellous bone material. Accordingly, when these bone pins are applied in their intended manner they substantially obviate the concern of pin tract infection by use of the fixators.
One problem noted with these generally non-invasive fixation devices is the use of high-force actuators or applicators such as by levers and the like that reduce the user's ability to sense or feel the level of force with which the pins are brought into engagement with the bones and the position at which the pin is engaged with the bone. For example, U.S. Pat. Nos. 6,030,387 and 6,283,965 to Ballier disclose a fixation device that utilizes an applicator gun for driving a displaceable bone pin into engagement with a bone, as by pulling or pivoting the pistol trigger thereof. Pulling the trigger causes a plunger to be driven into engagement with the bone pin for advancing it toward the bone. The applicator pistol can generate forces that are sufficiently high to drive the pin all the way through the tibia. Further, the external arch to which the bone pin is supported is received in a slot at the far end of the barrel of the applicator pistol so that the user's hand generating the application force is somewhat removed from the bone pin and the patient into which it is being applied. This arrangement with the arch cantilevered off the front end of the gun makes it difficult for the user to manipulate the arch into proper position and to control the apparatus during the application process due to the heavy front-loaded weight of the entire apparatus. Further, the user has very little feel or sensory input as to whether there was good anatomical placement of the pin on the bone and the level of force with which the pin was engaged with the bone. As the applicator pistol is not designed to stay with the fixator arch and pins gripped on the bone during healing, further complexities are necessarily added to the Ballier apparatus by the releasable latching mechanism provided between the gun and the arch.
Another shortcoming with fixation devices utilizing non-invasive bone pins involves their stability since the pins are not anchored through the bone. These devices have connecting rods that extend between two such devices having their pins secured onto a bone. In the Ballier devices, for example, the arches have ball receptacles through which the connecting rods are passed and clamped therein after the bone fracture has been reduced for setting the bone in place for healing. The commercial Ballier fixator has these receptacles spaced by approximately 2½ inches and by an angular spacing about a center axis of the bone of approximately 50 degrees. The clamping balls of a Ballier arch are both clamped onto the rods passing therethrough by a single plate. Thus, increasing the separation between the balls entails a corresponding increase in the size of the clamping plate creating extra weight for the apparatus. Extra weight is undesirable from both an application standpoint as earlier considered, as well as from a patient's perspective who will usually have to wear the device for several days during the bone-healing process.
The problem with the small separation of the connecting rods is that the rod connected fixators tend to lack stability as they approach a coplanar relation with the bone axis. In other words, the closer the rods are together, the less stable the whole bone fixation system becomes; similarly, as the angular spacing of the connecting rods approaches 180 degrees, and thus again approximating a coplanar relation with each other, stability in directions transverse to the planes between the rods and bone is lost. With the current Ballier fixators having the above-described small separation and the relatively small angular spacing therebetween, the overall fixation system lacks the rigidity and stability that is desired.
Accordingly, there is a need for an ergonomic and easier-to-use fixation apparatus and method for advancing bone pins into gripping engagement with bone surfaces. An apparatus and method that provides a user with high resolution feel of the engagement forces and placement of the pin on the bone would be desirable. Further, a bone fixation system that has maximum stability as fixed to a bone is needed.